Electronic Structure Modulation in GeTe by Hg and Sb Codoping Leads to High Thermoelectric Performance.

Area of Science:

• Materials Science
• Solid State Physics
• Thermoelectrics

Background:

• Germanium telluride (GeTe) is a promising thermoelectric material, but its performance is limited by high carrier concentration and lattice thermal conductivity.
• Optimizing electronic band structure and introducing midgap states are key strategies for enhancing thermoelectric figure of merit (zT).

Purpose of the Study:

• To improve the thermoelectric performance of GeTe by codoping with Hg and Sb.
• To investigate the effects of Hg and Sb codoping on the electronic band structure and lattice thermal conductivity of GeTe.

Main Methods:

• Synthesis of Hg and Sb codoped GeTe.
• Experimental characterization of thermoelectric properties (Seebeck coefficient, electrical conductivity, thermal conductivity).
• First-principles density functional theory (DFT) calculations for electronic band structure analysis.
• Pisarenko analysis to study the electronic density of states.
• Fabrication and testing of a double-leg thermoelectric device.

Main Results:

• Achieved a thermoelectric figure of merit (zT) of ~2.4 at 727 K in Hg and Sb codoped GeTe.
• Hg doping facilitated valence band convergence and introduced a hybridized midgap band, enhancing the Seebeck coefficient.
• Sb codoping localized the midgap state and shifted the Fermi level, further boosting the Seebeck coefficient.
• HgTe nanoprecipitates formed above the solid solution limit, significantly reducing lattice thermal conductivity.
• A thermoelectric device demonstrated a promising output power density of 0.77 W/cm².

Conclusions:

• Synergistic effects of electronic structure optimization and lattice thermal conductivity reduction in Hg and Sb codoped GeTe lead to high thermoelectric performance.
• The developed material shows significant potential for high-performance thermoelectric power generation applications.